when I started quilting I had the same issue. The more you do, the better you will get, just like anything else. Being off 1/8" would be significant on some patterns but not on others. Work on two things--first accurate cutting, and second an accurate and consistent 1/4" seam allowance. Errors in either of these will cause your variances. And we all have them from time to time---that is why we have seam rippers!!
